Various techniques have been devised to align objects in proper two-dimensional relationship. For example, U.S. Pat. No. 2,701,501 discloses techniques for testing the axial alignment of an object with respect to an optical reference axis which is coincident with the geometrical axis of the supporting structure. U.S. Pat. No. 3,349,664 discloses techniques useful for properly aligning objects to check the pointing and mounting mechanism of a telescope. Two-dimensional alignment of the telescope with respect to a mirror is checked by verifying that the optical axis of the telescope is perpendicular to the mirror, so that light rays reflected off the mirror converge at the focal point and are sensed by a photo tube. U.S. Pat. No. 3,994,588 discloses techniques useful for torque measuring instruments to detect angular deflections of one object with respect to another. The uniform distribution of light reflected by a mirror back to photo detectors indicates a null position when the mirror is perpendicular to the optical axis of a light-emitting diode.
The proper alignment of objects is particularly critical in outer space applications. One object, such as a spacecraft manipulator arm, must be properly aligned for docking with another object to accomplish basic space operations. U.S. Pat. No. 3,910,533 teaches a docking alignment device suitable for aligning two spacecraft. A TV camera is mounted on one craft for viewing a three-dimensional target on the other craft. An image of the target is thus displayed on a TV monitor, so that three-dimensional traverse alignment of one craft relative to the other is possible. U.S. Pat. No. 4,349,837 discloses a similar system for alignment and docking of two objects in space, with a monitor displaying images from a TV fixed on one object and the monitor having markings for visual alignment with a target on the other object to be docked. The target may be proportioned with respect to the markings on the monitor so that the size of the target image and the two-dimensional alignment of the markings on the monitor and the target allow for three-dimensional traverse alignment of the objects. U.S. Pat. No. 4,395,005 teaches the use of fiber optic cables for aligning spacecraft, wherein one of the cables conveys light from a source to a docking location, and a second cable conveys an image of the docking location to a TV camera. U.S. Pat. Nos. 4,177,964 and 4,621,924 generally disclose optical alignment systems suitable for outer space applications.
The prior art does not, however, teach a system to easily and accurately align two objects in space which encompasses both three-dimensional translational and three-dimensional rotational alignment of the objects. Three-dimensional translational alignment of the objects is particularly critical when multiple objects are stored one on top of the other, which must subsequently be selectively picked up by a computerized or manually operated manipulator system. Also, preferred docking techniques preferably allow for independent three-dimensional translational alignment of two objects and three-dimensional rotational alignment of the objects. Moreover, proper alignment is preferably accomplished by a technique which is easily automated and provides high alignment accuracy.
The disadvantages of the prior art are overcome by the present invention, and a relatively simple yet reliable technique is hereinafter disclosed for properly aligning objects. The technique of the present invention is particularly well suited for aligning objects in outer space where proper three-dimensional translational and three-dimensional rotational alignment of the objects is necessary.